High Strength Steel

ABSTRACT

A steel composition that includes: about 0.25-0.37% by weight Carbon; about 1.20-1.55% by weight Manganese; about 0.1-0.15% by weight Vanadium; about 0.20-0.40% by weight Nickel; about 0.20-0.50% by weight Silicon; about 0.30-0.45% by weight Copper; about 0.017-0.025% by weight Nitrogen; and Iron as the main constituent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 11/375,186which is a continuation-in-part of U.S. application Ser. No. 11/092,434,filed Mar. 29, 2005, which claims priority to U.S. provisionalapplication No. 60/557,367, filed Mar. 29, 2004, all of which are reliedon and incorporated by reference.

BACKGROUND

Articles such as anchor bolts are used in the utility industry to securetransmission poles to concrete bases. Such articles require a strongmaterial that exhibits good low temperature impact strength. Onesuitable material for such articles is steel having a minimum Charpyv-notch impact strength at 20F of 15 Ft-1b and minimum yield strength of75,000 psi. Such steels are typically manufactured according to aprocess that involves normalizing the steel in a furnace at hightemperatures, followed by a separate, high temperature temperingtreatment, to ensure production of steels that consistently have therequired mechanical properties.

DETAILED DESCRIPTION OF THE INVENTION

Advantageous steel compositions are described that include iron as themain constituent and the following additional elements:

(a) about 0.25-0.37% (preferably about 0.30-0.34%, more preferably about0.30-0.32%) by weight carbon;

(b) about 1.20-1.55% (preferably about 1.25-1.50%, more preferably about1.35-1.45%) by weight manganese;

(c) about 0.1-0.15% (preferably about 0.11-0.14%) by weight vanadium;

(d) about 0.20-0.40% by weight nickel;

(e) about 0.20-0.50% by weight silicon;

(f) about 0.30-0.45% by weight copper; and

(g) about 0.017-0.025% (preferably about 0.018-0.022%, more preferablyabout 0.019-0.021%) by weight nitrogen. The composition may also includeone or more of the following elements:

(h) up to about 0.30% (preferably up to about 0.25%, more preferably upto about 0.20%) by weight chromium;

(i) up to about 0.035% (preferably up to about 0.025%, more preferablyup to about 0.020%) by weight phosphorus;

(j) up to about 0.04% by weight sulfur (preferably up to about 0.02%);

(k) up to about 0.06% by weight tin; and/or

(l) up to about 0.06% (preferably up to about 0.04%) by weightmolybdenum.

In some embodiments, Ti, Nb and Al can be present individually or incombination in amounts of up to 0.025% by weight Ti, up to 0.025% byweight Nb and up to 0.04% Al.

Other elements may also be present in the steel in low percentages.

To prepare steel having good mechanical properties (e.g., steels havinggood low temperature impact strength coupled with high yield and tensilestrength such as 75S steel), the above-described steel composition ischarged to a furnace, where it is normalized by heating the compositionat a furnace temperature between about 1500° F. and about 1650° F.Optionally, the composition may be further treated by tempering thecomposition by heating at a furnace temperature between about 850° F.and about 1000° F. However, one advantage of the composition is thatsteels having mechanical properties sufficient for applications such asanchor bolts may be consistently produced without the separate temperingstep. The ability to eliminate the tempering step, in turn, reduces theoverall cost of producing the steel product.

Minor amounts of other elements may also be present in the steel.

The individual effect of the various elements in an alloy is obscured bythe presence of other elements. Together, the combination of elements inthe steel alloy provides the desired properties. Although the individualeffect of the elements cannot be easily isolated from the combinedeffect of the alloy, it is generally recognized that certain elementswill have certain effects. The various elements and their generallyrecognized effects can be described as follows.

Iron, Fe, is the main element in steel.

Carbon, C, is a principal element responsible for hardness in steel anda wide range of other properties including strength, ductility, impactstrength, etc. Generally, carbon increases tensile strength anddecreases ductility.

Manganese, Mn, as an element in steel generally increases hardenability,toughness, and tensile strength of the steel, though it may decreaseductility. Manganese helps in stabilizing steel microstructures andhelps prevent degradation of iron carbide structures to iron andgraphite. Manganese can also help offset negative effects of otherelements, and can assist in reducing brittleness and possible tearing ofthe steel.

Silicon, Si, acts as a deoxidizer of steel. Silicon can improve tensilestrength, but reduces machinability and can promote graphitization.

Copper, Cu, can cause tearing and poor surface quality of the steel.Cooper can stiffen the steel, but decreases ductility. Cooper alsoimparts corrosion resistance to the steel.

Nickel, Ni, improves hardenability and stiffens steel, but it decreasesductility. Nickel acts to reduce distortion in heat-treating and enablesmilder quenching. Nickel also improves fatigue properties, toughness,corrosion resistance, and also improves the surface quality of steel.

Chromium, Cr, improves wear resistance and improves the resistance tosoftening during heat-treating. Chromium also stiffens steel and reducesductility and improves hardenability, but can increase the brittlenessof steel.

Molybdenum, Mo, can greatly increase hardenability. It also increasesstiffness and decreases ductility. Molybdenum can improve control ofheat treatment by inhibiting formation of certain steel microstructures.It can also increase corrosion resistance, toughness, and fatigueproperties. Molybdenum can also be particularly expensive.

Vanadium, V, can help control the steel grain size and reduces thegrowth of austenite structures. Vanadium also improves abrasionresistance, and improves yield strength, toughness, and hardness. Italso can be particularly expensive.

Nitrogen, N, can increase the strength of steel and improve weldability.It also increases brittleness and can lead to increased porosity of thesteel.

Phosphorus, P, can improve hardenability and corrosion resistance. Italso can improve machinability of the steel. However, it decreasesductility and impact strength, sometimes significantly. Control ofphosphorus content can also affect the required heat time in steelpreparation.

Sulfur, S, is used to improve machinability. Generally, it decreasesimpact strength, ductility, and weldability. It also can decreasesurface quality and may lead to tearing.

Tin, Sn, is generally used to coat steels. As an alloy element, Tindecreases surface quality and may lead to tearing. It also increasesbrittleness of the steel.

Titanium, Ti, and Niobium, Nb, provide grain refinement, precipitationstrengthening and sulfide shape control by forming a number of compoundslike nitrides and carbides. Titanium and Aluminum, Al, act as strongdeoxiders of steel as well. This group of elements improves yieldstrength and toughness.

To produce steel having useful mechanical properties suitable forapplications such as anchor bolts, the composition is charged to afurnace, where it is normalized by heating the composition at a furnacetemperature between about 1500° F. and about 1650° F. The compositionmay be in the form of, for example, bars, ingots, plates, sheets, or thelike. The composition, if desired, may be further treated by temperingthe composition by heating at a furnace temperature between about 850°F. and about 1000F. However, the tempering is not required and ispreferably eliminated, thereby lowering overall production costs.

The normalization step may be performed by charging the composition atan initial furnace temperature at about 1600° F., and then lowering thefurnace temperature to a furnace temperature at about 1500° F. once thecomposition temperature approaches 1500° F. In one approach, thecomposition is held at the initial furnace temperature for about 15 to30 minutes, and then held at the second furnace temperature for about 30to 45 minutes. The first part of the process can be referred to as the“thermal head,” while the second part can be referred to as the “soak.”

Another alternative for normalizing includes charging the composition atan initial furnace temperature at about 1500° F., and maintaining thefurnace temperature at about 1500° F. once the composition temperatureapproaches 1500° F. This alternative only uses the soak portion of theprocess. The process will work in such a manner, but the time must beincreased accordingly.

In another alternative, a shorter or longer thermal head time may beutilized, with the time depending on the first temperature of thefurnace. In summary, the process heats the bars above the transformationtemperature (typically about 1450° F.), and keeps them at that highertemperature for some time.

Also, the normalizing temperature used depends on the specificchemistry, or combination of elements, of the steel, though temperaturesin the range of about 1500° F. to about 1650° F. are expected. Dependingon the composition, the initial furnace temperature and second furnacetemperature will vary from the example discussed above. For instance, inanother alternative, the first initial furnace temperature may be 1625°F. When the composition surface temperature approaches 1525° F., thenthe furnace temperature is reduced to 1525° F. to complete thenormalizing. Following normalization, the product exits the furnace andis allowed to cool on an exit conveyor.

In one embodiment, a steel reinforcing bar may be created using arolling process from the composition. The bar meets or exceeds therequirements of ASTM A615 Standard Specification for Deformed and PlainBillet-Steel Bars for Concrete Reinforcement, which are as follows:

Minimum Yield Strength (ASTM A370-03a): 75,000 psi;

Minimum Tensile Strength (ASTM A370-03a): 100,000 psi;

Minimum Elongation (ASTM A370-03a): 10%;

Bend Test 9d Pin (ASTM A370-03a): 90 degrees;

In addition, the bar exhibits a minimum Charpy V-Notch Impact Strengthat −20° F. (ASTM A673) of at least 15 ft-1b.

The invention will now be described further by way of the followingexamples.

Example 1

Heat S61270, with a grade description of 75S-M5, had a compositionincluding iron and other untested elements as well as the followingelements with their amounts:

Element % C 0.32 Mn 1.43 P 0.02 S 0.018 Si 0.42 Sn 0.01 Cu 0.33 Ni 0.25Cr 0.18 Mo 0.04 Cb 0.002 Al 0.001 N 0.02 Co 0.01 Ti 0.003 V 0.132 Ca0.0007

This composition was formed into bars and then charged to a furnace withan atmospheric temperature of about 1600° F. The bars were allowed toheat until the surface of the bars approached about 1500° F. Thisheating required about 20 minutes. Then, the temperature of the furnacewas reduced to about 1500° F. The bars were held at this temperature forabout 35 minutes. Thereafter, the bars exited the furnace and wereallowed to cool on the exit conveyor.

The composition was then tested. The yield strength of the compositionwas 81.7 k.p.s.i. and the tensile strength was 108.3 k.p.s.i.Additionally, the composition has an elongation test result of 20.63%and the Charpy impact strength was 35.5 ft-lbs.

Example 2

Heat S73516, with a grade description of 75S-M7, had a compositionincluding iron and other untested elements as well as the followingelements with their amounts:

Element % C 0.32 Mn 1.40 P 0.012 S 0.009 Si 0.23 Sn 0.018 Cu 0.32 Ni0.24 Cr 0.11 Mo 0.034 Cb 0.002 Al 0.002 N 0.0191 Co 0.011 Ti 0.003 V0.144 Ca 0.0012

This composition was formed into bars and then charged to a furnace withan atmospheric temperature of about 1600° F. The bars were allowed toheat until the surface of the bars approached about 1500° F. Thisheating required about 20 minutes. Then, the temperature of the furnacewas reduced to about 1500° F. The bars were held at this temperature forabout 35 minutes. Thereafter, the bars exited the furnace and wereallowed to cool on the exit conveyor.

The composition was then tested. The yield strength of the compositionwas 80.7 k.p.s.i. and the tensile strength was 105.5 k.p.s.i.Additionally, the composition has an elongation test result of 18.8% (8inch gage length) and the Charpy impact strength was 30.8 ft-lbs.

Example 3

Heat S74110, with a grade description of 75S-M7, had a compositionincluding iron and other untested elements as well as the followingelements with their amounts:

Element % C 0.31 Mn 1.41 P 0.012 S 0.012 Si 0.26 Sn 0.01 Cu 0.35 Ni 0.33Cr 0.14 Mo 0.04 Cb 0.001 Al 0.001 N 0.0197 Co 0.01 Ti 0.003 V 0.149 Ca0.0021

This composition was formed into bars and then charged to a furnace withan atmospheric temperature of about 1600° F. The bars were allowed toheat until the surface of the bars approached about 1500° F. Thisheating required about 20 minutes. Then, the temperature of the furnacewas reduced to about 1500° F. The bars were held at this temperature forabout 35 minutes. Thereafter, the bars exited the furnace and wereallowed to cool on the exit conveyor.

The composition was then tested. The yield strength of the compositionwas 78.7 k.p.s.i. and the tensile strength was 107.8 k.p.s.i.Additionally, the composition has an elongation test result of 20.6% (8inch gage length) and the Charpy impact strength was 25.5 ft-lbs.

Example 4

Heat S74248, with a grade description of 75S-M7, had a compositionincluding iron and other untested elements as well as the followingelements with their amounts:

Element % C 0.30 Mn 1.41 P 0.011 S 0.012 Si 0.22 Sn 0.004 Cu 0.32 Ni0.36 Cr 0.18 Mo 0.03 Cb 0.001 Al 0.002 N 0.0201 Co 0.01 Ti 0.002 V 0.141Ca 0.0015

This composition was formed into bars and then charged to a furnace withan atmospheric temperature of about 1600° F. The bars were allowed toheat until the surface of the bars approached about 1500° F. Thisheating required about 20 minutes. Then, the temperature of the furnacewas reduced to about 1500° F. The bars were held at this temperature forabout 35 minutes. Thereafter, the bars exited the furnace and wereallowed to cool on the exit conveyor.

The composition was then tested. The yield strength of the compositionwas 85.6 k.p.s.i. and the tensile strength was 111.4 k.p.s.i.Additionally, the composition has an elongation test result of 17.8% (8inch gage length) and the Charpy impact strength was 36.2 ft-lbs.

A number of embodiments of the invention have been described.Nevertheless, it will be understood the various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. A steel anchor bolt, comprising: about 0.25-0.37% by weight Carbon; about 1.20-1.55% by weight Manganese; about 0.1-0.15% by weight Vanadium; about 0.20-0.30% by weight Nickel; up to about 0.50% by weight Silicon; about 0.30-0.45% by weight Copper; about 0.017-0.025% by weight Nitrogen; and Iron as the main constituent.
 2. The steel anchor bolt of claim 1, further comprising: from above zero up to about 0.30% by weight Chromium; from above zero up to about 0.035% by weight Phosphorus; from above zero up to about 0.04% by weight Sulfur; from above zero up to about 0.06% by weight Tin; and from above zero up to about 0.06% by weight Molybdenum.
 3. The steel anchor bolt of claim 1, wherein said steel anchor bolt meets the requirements of 75S steel.
 4. The steel anchor bolt of claim 1, further comprising: from above zero up to about 0.035% by weight Phosphorus.
 5. The steel anchor bolt of claim 1, further compromising: from above zero up to about 0.04% by weight Sulfur.
 6. The steel anchor bolt of claim 1, further comprising: from above zero up to about 0.06% by weight Tin.
 7. The steel anchor bolt of claim 1, further comprising: from above zero up to about 0.06% by weight Molybdenum.
 8. The steel anchor bolt of claim 1 having a steel composition comprising: about 0.30-0.34% by weight Carbon; about 1.25-1.50% by weight Manganese; about 0.1-0.15% by weight Vanadium; about 0.20-0.30% by weight Nickel; about 0.20 0-0.50% by weight Silicon; about 0.30-0.45% by weight Copper; about 0.018-0.022% by weight Nitrogen; and Iron as the main constituent.
 9. The steel anchor bolt of claim 8, further comprising: from above zero up to about 0.25% by weight Chromium.
 10. The steel anchor bolt of claim 8, further comprising: from above zero up to about 0.25% by weight Chromium; from above zero up to about 0.025% by weight Phosphorus; from above zero up to about 0.04% by weight Sulfur; from above zero up to about 0.06% by weight Tin; and from above zero up to about 0.06% by weight Molybdenum.
 11. The steel anchor bolt of claim 1, comprising: about 0.30-0.32% by weight Carbon; about 1.35-1.45% by weight Manganese; about 0.11-0.14% by weight by Vanadium; about 0.20-0.30% by weight Nickel; about 0.35-0.45% by weight Silicon; about 0.30-0.45% by weight Copper; about 0.019-0.021% by weight Nitrogen; and Iron as the main constituent.
 12. The steel anchor bolt of claim 11, further comprising: from above zero up to about 0.20% by weight Chromium.
 13. The steel anchor bolt of claim 11, further comprising: from above zero up to about 0.20% by weight Chromium; from above zero up to about 0.02% by weight Phosphorus; from above zero up to about 0.02% by weight Sulfur; from above zero up to about 0.06% by weight Tin; and from above zero up to about 0.04% by weight Molybdenum.
 14. The steel anchor bolt of claim 1, further comprising from above zero up to about 0.025% by weight Titanium; from above zero up to about 0.025% by weight Niobium; and from above zero up to about 0.04% by weight Aluminum.
 15. The steel anchor bolt of claim 1, further comprising from above zero up to about 0.025% by weight Titanium.
 16. The steel anchor bolt of claim 15, further comprising from above zero up to about 0.04% by weight Aluminum.
 17. The steel anchor bolt of claim 15, further comprising from above zero up to about 0.025% by weight Niobium.
 18. The steel anchor bolt of claim 1, further comprising from above zero up to about 0.025% by weight Niobium.
 19. The steel anchor bolt of claim 18, further comprising from above zero up to about 0.04% by weight Aluminum.
 20. The steel anchor bolt of claim 1, further comprising from above zero up to about 0.04% by weight Aluminum.
 21. A steel anchor bolt made by a method comprising: (a) providing a steel composition, comprising: about 0.25-0.37% by weight Carbon; about 1.20-1.55% by weight Manganese; about 0.1-0.15% by weight Vanadium; about 0.20-0.30% by weight Nickel; up to about 0.50% by weight Silicon; about 0.30-0.45% by weight Copper; about 0.017-0.025% by weight Nitrogen; and Iron as the main constituent. (b) charging the composition into a furnace; and (c) normalizing the composition by heating at a furnace temperature between about 1500.degree.F. and about 1650.degree.F.
 22. The steel anchor bolt of claim 21, wherein the steel comprises a 75S steel.
 23. The steel anchor bolt of claim 21 wherein the method o further comprises: (d) tempering the composition by heating at a furnace temperature between about 850.degree. F. and about 1000.degree.F.
 24. The steel anchor bolt of claim 21, wherein the normalizing step of the method comprises: charging the composition at an initial furnace temperature at about 1600.degree.F.; and lowering the furnace temperature to a furnace temperature at about 1500.degree.F. once the composition temperature approaches 1500.degree.F.
 25. The steel anchor bolt of claim 24, wherein the composition is held at the initial furnace temperature for about 15 to 30 minutes, and wherein the composition is held at the second furnace temperature for about 30 to 45 minutes.
 26. The steel anchor bolt of claim 21, wherein the steel composition provided is in the form of bars or ingots
 27. The steel anchor bolt of claim 21, wherein the normalizing step of the method comprises: charging the composition at an initial furnace temperature at about 1500.degree. F.; and maintaining the furnace temperature at about 1500.degree.F. once the composition temperature approaches 1500.degree.F.
 28. The steel anchor bolt of claim 21, further comprising: (d) cooling the composition in air. 